It is a black sponge with vicious blood-red eyes and deadly white sharp teeth.
Role in the series
The Evil Manta unleashes the Brain Sponge as his final means to rid himself and his son of Ariel who sees good in him. Little Evil couldn't allow his new friend to lose her imagination to the Brain Sponge and releases Ariel from his father's trap panicked upon seeing that it was also targeting Little Evil. In an attempt to save his son, Evil Manta would push both Little Evil and Ariel out of the way before the monster had the chance to strike, the Brain Sponge latching onto and draining the life force from Manta instead. With Ariel and Little Evil's help, they free Evil Manta from the Brain Sponge and crushing it with a large rock.